Various terms are defined in the following specification. For convenience, a Glossary of terms is provided herein, immediately preceding the claims.
Laws such as the Clean Air Act (1990) and the Energy Policy Act (1992), which mandate the purchase of alternative fueled vehicles (AFVs), have spurred several serious business initiatives to develop natural gas vehicles (NGVs). Although these laws were motivated by air quality issues, they have created economic incentives that have spurred real activity in implementing NGVs. NGVs currently hold the most competitive potential alternative to gasoline-powered vehicles because of the inherent clean-burning characteristics of natural gas.
Three competing technologies for the implementation of NGV-type AFVs are: compressed natural gas (CNG), liquefied natural gas (LNG), and liquefied petroleum gas (LPG). In CNG technology, the gaseous (natural gas) fuel is stored at very high pressures of about 20684 kPa to 24132 kPa (3000-3500 psia). There are at least four major shortcomings of CNG technology that have limited its successful deployment: short vehicle driving range (due to low energy storage per fuel storage container volume); safety issues associated with the high storage pressures; the weight and high cost of the on-board (and typically non-conformable) fuel storage containers; and the high cost of the refueling stations which must include high pressure ratio compression systems. LNG technology overcomes the low energy density limitation of CNG in that much more energy can be stored per unit volume. Other advantages of LNG over CNG include lower vehicle fuel system weight and higher fuel storage volume capability. For example, the weight of a typical on-board fuel storage system filled with CNG is over 2.5 times that of a typical LNG system. However, the extremely cold storage temperature of 162.degree. C. (-260.degree. F.) required for an LNG system results in high costs of the fuel storage containers which are typically made out of expensive special alloys, such as commercial nickel-containing steels (e.g., 9 wt % nickel), or aluminum alloys (e.g., Al-5083). Further, the need to deliver pressurized natural gas to an engine's fuel injectors adds to the complexity and cost of the fuel delivery system. A recent solicitation from the DOE's Brookhaven National Laboratory on LNG technology for NGV's highlights the need for an LNG delivery system for medium-pressure fuel injectors. An alternative to LNG with similar clean burning characteristics is liquefied petroleum gas (LPG). LPG overcomes the limitations of both CNG and LNG in that LPG offers higher energy storage per vessel volume than either CNG or LNG and operates at relatively low pressures (about 827 kPa (120 psia)), as compared to CNG, and at ambient temperatures. However, LPG supply is limited and LPG is much more expensive than LNG.
A co-pending U.S. patent Applications (the "PLNG Patent Applications"), entitled "Improved System for Processing, Storing, and Transporting Liquefied Natural Gas", describes containers and tanker ships for storage and marine transportation of pressurized liquefied natural gas (PLNG) at a pressure in the broad range of about 1035 kPa (150 psia) to about 7590 kPa (1100 psia) and at a temperature in the broad range of about -123.degree. C. (-190.degree. F.) to about -62.degree. C. (-80.degree. F.). The PLNG Patent Application has a priority date of Jun. 20, 1997 and is identified by the United States Patent and Trademark Office ("USPTO") as Application No. 09/099268 and has been published in WO 98/59085. Additionally, the PLNG Patent Application describe systems and containers for processing, storing, and transporting PLNG.
PLNG offers an alternative, cost-effective vehicular fuel source that provides the clean-burning advantages of CNG, LNG, and LPG. In addition, PLNG offers higher energy storage per fuel storage container volume than CNG, is less expensive to process than LNG, and overcomes the limited supply disadvantage of LPG. However, to our knowledge, no fuel storage and delivery systems are currently available for economically storing PLNG fuel and delivering vaporized PLNG fuel on demand for combustion in a vehicle engine. If such a fuel storage and delivery system were available, PLNG would offer a vehicular fuel source that overcomes the principal disadvantages of CNG, LNG, and LPG. A need exists for a fuel storage and delivery system to economically store PLNG fuel and deliver vaporized PLNG fuel on demand for combustion in an engine.
Consequently, the primary object of the present invention is to provide fuel storage and delivery systems suitable for storing PLNG fuel and delivering vaporized PLNG fuel on demand for combustion in an engine.